Circular type sawblades to cut cants or lumber are, of course, known together with their associated drive splines. Typically, the drive spline has a series of rounded or convex male drive pieces spaced intermittently and circumferentially around the drive spline. They mate with corresponding concave female recesses in the saw blade. Typically, the sawblade is mounted onto the drive spline endwise. It slides over the spline until the desired operating position on the drive spline is reached. Under operating conditions, the sawblade is maintained in its desired position with sawguides which prevent undesirable movement in the sawblade. This keeps the kerf or cutting width created by the blade narrow which is desirable in order not to avoid wood wastage during the sawing operation.
The drive spline used with the aforementioned convex male driving pieces has problems. Such problems relate to safety, tolerances and sawblade driving efficiency.
In respect of the former, there has arisen the unfortunate practise of "tree spiking" by those protective of logs which they feel should not be felled. This practise involves driving large nails or spikes into the trunks of trees before cutting. Often the spikes are not readily observed by either the fellers or the sawmill operators with the result that during sawmill operations, the sawblade may strike a spike within the cant or log during the cutting operation. This is a most dangerous occurrence since the sawblade can tear or fragment and pieces of shrapnel are distributed at high energy levels throughout the area where the cutting is taking place. This disintegration takes place because there is no retention of the sawblade by the spline when the sawblade splits or tears after contact with the spike. Sawmill operators lives have been lost and their injuries have been severe because of these tree spiking practises. It would be advantageous if the sawblade did not tear away from the drive spline under such conditions.
Yet a further disadvantage with present sawblades and the convex type drive splines relates to operating tolerances. Because of the convex type drive spline which mates with corresponding type recesses in the sawblade, a series of point contacts occurs when the two curved surfaces meet. This point contact results in a series of high stress points between the drive spline and the sawblade which increases wear on both members and reduces the driving efficiency between the spline and the sawblade.
Yet a further disadvantage with the present sawblade-drive spline system is that the position of the sawblade on the drive spline can change during operation. This is so because there are tolerances between the convex drive surfaces of the drive spline and the concave driven surfaces of the sawblade. The saw blade will move upwardly and downwardly on the spline during operation while various impact loadings occur and the sawblade moves upwardly and downwardly on the spline through these tolerances. Thus, the actual driving efficiency is adversely affected.
Yet a further disadvantage with the present drive spline design is the fact that the spline has to be hardened to a hardness greater than that of the blade. This practise is time consuming and expensive.